This invention relates to an annular, tubular, columnar, ring-shaped and belt-shaped cylindrical article such as a conveyor belt used to convey precision parts to a predetermined location while maintaining a high degree of positional accuracy, or a sealed package for packaging and accommodating an article. The invention further relates to a method of manufacturing the cylindrical article. The principal field in which the invention is utilized resides in application of the article as the functional component of an image forming apparatus.
More particularly, the invention provides a method of forming a fluoroplastic film on a tubular film used as a cylindrically shaped article and relates to use of this article as a fixing member for image formation.
The following methods of forming a fluoroplastic film on the inner peripheral surface or outer peripheral surface of an article (especially a tubular film made of resin) having a cylindrical shape are known in art:
(1) A method of applying a coating by a process such as spray coating or dip coating for applying fluoroplastic particles or a solution in which fluoroplastic particles have been dispersed, drying the solvent and applying heating to calcine the fluoroplastic film.
(2) A method of covering the outer side of a cylindrically shaped body with a heat-shrinkable fluoroplastic tube and then heating the entirety.
Further, the following method has been proposed previously by the applicant:
(3) A method of winding a sheet-like film consisting of a thermoplastic resin and a sheet-like film consisting of a fluoroplastic on a columnar member in such a manner that the leading and trailing edges of the films overlap, fitting a tubular member over the two-layered film thus wound, subsequently heating the whole to bond the overlapping portions of the films and fuse the film layers, thereby obtaining a tubular film comprising the two layers, namely the fluoroplastic film layer and the base layer.
By making the coefficient of thermal expansion of the columnar member larger than that of the tubular member, the gap between them diminishes when heating is applied, the step or difference in level at the overlapping portions vanishes and a uniform film thickness is achieved over the entire circumference. In addition, controlling the gap makes it possible to control the overall film thickness at will.
However, the examples of the prior art mentioned above certain disadvantages. Specifically, in method (1) of applying a coating of the fluoroplastic particles, drying the coating and then calcining the same, it is required that a high temperature be maintained for a prescribed period of time when the fluoroplastic is calcined. For example, the temperature is on the order of 400.degree. C. for PTFE (polytetrafluoroethylene) and 350.degree. C. for PFA (a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether). In a case where a resin is used as the base, it is required that this exhibit resistance to heat. Further, even if the resin is capable of withstanding the high temperatures cited above, the resin undergoes heat deterioration, deformation caused by relaxation of internal stress and surface roughness due to the formation of bubbles caused by water content.
Difficulties similar to those encountered in method (1) also arise with the method (2), in which use is made of the fluoroplastic tube covering.
Further, in a case where the fluoroplastic tube or fluoroplastic film sheet is used, as in methods (2) and (3) above, and a fluoroplastic layer having a thickness of less than 20 .mu.m is formed, it is required that the tube or sheet have a corresponding thickness. However, manufacturing such a tube or sheet is difficult.
Many fluoroplastic tubes and sheets currently available on the market have a thickness of greater than 20 .mu.m. Manufacturing tubes or sheets having a smaller thickness raises cost and results in an article of higher price.